Replacing driver screws with brass screws

@cal91,

'I am a Harbeth owner and I don't see how I could do that with the screws securing my drivers.'


As an Harbeth owner perhaps it might help to be a little more familiar with the Harbeth website?

Alan Shaw stated that it's no big deal as long as you're sensible and use no more pressure than is required to meet resistance. 

Basically - Don't go mad!!

If you're really struggling I can try and dig up his exact words for you.


As for brass screws, let's not even go there!

How about simply trusting the manufacturers?

The people whose livelihoods depend upon their products.

The people who have spent a lot of time and resources building loudspeakers.

I might not like a lot of loudspeakers out there, but I'm not going to pretend for one moment that I, with my severely limited resources and knowledge, could do any better.

Seriously, if anyone is considering ruining their speakers in this way, it might be wise to contact the manufacturer first if they are of any value to you. 

Another word of caution against over-tightening of drive units.  

Don't do it.

As mentioned earlier it alters the tone, but it does more than that, it alters the amount of resonance pumped into the baffle. Since the baffle due to the cutouts is normally the weakest part of the cabinet, you certainly don't want more resonances there. 

With large drivers the issue becomes paramount.

Some, like Harbeth only recommend finger tight, and I tend to agree.

Over-tightening in my experience often results in an uptight and dynamically constrained sound. 

For sure there are better ways of attaching drive units to the baffle, but they are all more time consuming and more expensive to implement than simple wood screws.

Here's what Siegfried Linkwitz had to say on the subject.


Mounting a driver to a baffle

'Typically a loudspeaker driver has screw holes in its basket for mounting it to a baffle. Usually a sealing gasket is placed between the driver basket rim and the baffle. The driver becomes in effect stiffly clamped to the baffle.

This method sets up a mechanically resonant structure which is formed by the compliance of the basket and the mass of the magnet...

A) Drivers with a stamped metal baskets are prone to exhibit a high Q resonance when tightly clamped to the baffle. The magnet moves relative to the voice coil at the resonance frequency. Energy is stored and also readily transmitted from the moving mass of the cone into the cabinet.

B) Soft mounting the driver basket to the baffle using rubber grommets reduces the resonance frequency. A 2nd order lowpass filter is formed that reduces the transmission of vibration energy from the moving cone to the baffle and cabinet. The resonance must occur below the operating range of the driver.

C) If the driver is mounted from the magnet and the basket rim touches the baffle only softly, then the magnet-basket resonance cannot occur and the transmission of vibration energy into the baffle is minimized. The basket-magnet resonance can be measured with an accelerometer that is mounted to the magnet.

The drive signal is optimally a shaped toneburst.

Its energy is concentrated in a narrow frequency band. When tuned to the right frequency a long decay tail becomes visible on an oscilloscope. Often the resonance can be seen as a small bump in the driver's impedance curve in the few hundred Hz range. It should not be confused with the higher frequency bump due to cone breakup.

An early example of a box loudspeaker where a KEF B110 midrange/woofer driver magnet is clamped to a support structure. The clamp can be tightened from the outside of the box. The basket rim is floating.

Often the effects due to driver mounting are deemed to be of secondary importance to the overall sound quality of a loudspeaker. They are usually costly to remedy. They cannot be ignored when the goal is to design a loudspeaker of the highest accuracy.

http://www.linkwitzlab.com/frontiers_2.htm#N

@andrei_nz,

’I guess in theory it did - as in everything makes a difference, not that I heard a difference. Did it improve the sound? Again, I do not know - it was inaudible to me.’


In theory anything could make a theoretical sonic difference - the power supply, the room temperature, the heat in the voice coil, the type of solder used, the finish of the cabinets, the types of connectors used, or ... maybe even a butterfly flapping its wings in the Brazilian rainforest etc.

However, since we’re only human, perhaps it’s best to leave imagination behind for once and to stick to those differences that we can consistently identify, time and time again, with or without visual evidence.

Life is finite, and so is our hearing. So why keep wasting time experimenting in ways that could make things a lot worse?

Why risk stripping of the cabinet screw thread, or upsetting the manufacturers desired torque?

Because someone online who enjoys trying out tweaks recommends brass screws?

Is anyone surprised that the respected designer John Dunlavy laughed when it was suggested to him?

Is it really very likely that some amateur online knows more than highly qualified and experienced designers?

Are you really so willing to gamble on that likelihood?

One slip of the screwdriver and...

rixthetrick,

’If someone isn’t going to take the time to research it properly, and purchase appropriate tools and fasteners to correctly implement this technology - I totally agree with CD318 - just don’t.’



Yes, it just isn’t worth it.

As I mentioned earlier, and shown in the link to the excellent Siegfried Linkwitz site there are other ways of attaching the driver to the cabinet other than just screws.

If one was in the experimental mode (and not particularly attached to their speakers) they could try the method used previously by the likes of KEF and the BBC.

In this case the driver is attached to the back of the speaker cabinet by its magnet whilst the front of the driver is hardly making any contact with the baffle.

As you can see in his driver mounting resonances diagram, out of the 3 illustrated methods the least resonances occur with the rear magnet attached method. It’s tricky to implement but it sure looks like an improvement. It’s also interesting that Linkwitz might have looked at this issue as far back as November 1986 (or maybe someone else had going by the date pencilled in the diagram.).

My previous speakers used both wood screws and a soft brace behind the magnet for stability.

Some manufacturers do go to some trouble to avoid driver excited resonances in the baffle.

One popular method is to use a sub-baffle and screw the driver in from behind.

Some might to prefer using grommets.

Certainly worth considering for those brave souls who want to build their own.

https://www.linkwitzlab.com/frontiers_2.htm#N

@rixthetrick,

’That’s got nothing to do with glupson’s screws made of wood idea, right?’


I’m guessing that the difficulty of obtaining such screws would limit the likelihood of designers wishing to experiment with wood screws.

In practical terms steel screws are fairly universal, easy to implement, and are cost effective. Whether they are sufficient enough is down to the designer.

Let’s not forget that the loudspeaker market is an extremely competitive one, with literally hundreds of different companies with models to sell.

So is it not fair to assume that something as simple to implement as type of metal used, steel or brass, for the screws would have been considered in most cases?

We know that some major designers consider the choice of screw metal irrelevant.

Do we know of any that don’t?


As glupson asked earlier,

’Also, there is a mention of "tightened to spec" earlier. Do manufacturers publish those specifications?’

As far as I know they don’t. I know Harbeth suggest finger tight (up til resistance) but are we now suggesting that manufacturers should publish torque figures?

If so, should it be our responsibility to maintain that recommended torque ourselves? Or the dealers?

Is fleschler’s case with his Focus speakers which arrived by freight with very loose screws/drivers a one-off?

Do Focus Audio know about this, and what the implications for them might be?

What do Wilson, Magico, Tannoy, Zu, JBL, Revel, B&W, ATC, PMC, Vivid, Spendor, Sonus Faber etc have to say on this issue?

Years ago people used to hot rod and modify their cars, but now in the computer age, this no longer seems to be popular.

Doesn’t this also apply to computer designed loudspeakers?

On the other hand I’m happy to accept that some, possibly only a few, like yourself have been able to get good results through careful experimenting.

You know sometimes, getting a little carried away, I almost wish that loudspeaker design was something I had considered back in school. But then I start to consider all of the technical difficulties and then I have to bring that particular pipe dream to a conclusion.

roxy54,

’cd318,
Amusing post. What does it really matter who thinks what when it is relatively simple to just try it yourself and see what YOU think?’


I was kind of hoping that the answer would have been obvious by now.


’Before even considering the efficacy of wood in this application, I wonder if anyone thinks that it’s possible to make screws of wood; any species of wood.’

It is possible. I have seen some wood screws (and plastic) used in exceptional circumstances (not loudspeakers), but I imagine the manufacturing costs alone would be somewhat of a huge deterrent.

As for an explanation for any of the possible effects you claim to have heard, "detail in ambient trails, focus in general, complex harmonics in voices and stringed instruments, and instrumental separation" I would put more down to differences in torque and not the screw material difference between steel and brass.

I think most of us we would tend to still feel the same as you once did, ’because it seemed like one of those lunatic fringe ideas.’

Who in their right mind would consider trying this out on a pair of Harbeths, Revels, Tannoys, Wilson’s etc?